1. Field of the Invention
The present invention relates to a balancer apparatus for an engine. More particularly, the invention relates to a balancer apparatus which cancels out inertial force and/or inertial couple induced by the pistons, connecting rods and the like when the engine is running to thereby suppress or reduce vibration of the engine.
2. Description of the Related Art
When individual movable portions of an engine such as an automobile engine become off balance during operation of the engine, vibration occurs. Such vibrations generate noise and wear out or damage individual bearings. To overcome this shortcoming, a balancer is typically used to cancel the inertial force or inertial couple of the piston, the connecting rod, and the like to reduce the vibration of the engine.
A conventional balancer apparatus of this type is disclosed in, for example, U.S. Pat. No. 3,667,317. As shown in FIGS. 20 and 21, this balancer apparatus applies vibration suppressing force to a crank shaft 101. More specifically, a drive gear 103 is attached to an crank arm 102. A balancer case 105 having a rectangular frame is secured to a cylinder block below the drive gear 103.
A pair of support shafts 106 and 107 are secured across the balancer case 105. First and second driven gears 108 and 109 are rotatably supported on the support shafts 106 and 107. Similarly, first and second weights 110 and 111 supported by the respective shafts via bushings 112 and 113 respectively. Both weights 110 and 111 are attached such that they are rotatable together with the respective driven gears 108 and 109. The drive gear 103 engages the first driven gear 108, which in turn engages the second driven gear 109. Accordingly, rotation of the crank shaft 101 is transmitted to the drive gear 103, to the first driven gear 108, and then to the second driven gear 109. Thus, as the first and second weights 110 and Ill rotate, a load to suppress the vibration of the engine acts on the crank shaft 101.
Efforts are continually being made to reduce the size of individual engine components and the balancer apparatus is no exception. As one means to make the balancer more compact, the weights 110 and 111 may be disposed in close proximity to the crank shaft 101. However, the weights 110 and 111 can not be arranged too close to the crank shaft 101, since they would interfere with the movement of connecting rod 114.
In another design modification, a counter weight 115 may be formed on the crank arm 102, as indicated by a double-dot chain line in FIG. 20, In this case the weight 110 (111) interferes with the counter weight 115. To prevent the interference of the weight 110 (111) with the counter weight 115 or connecting rod 114, the weight 110 (111) needs to be provided in close proximity to the crank shaft 101. This restricts the horizontal length of the weight 110 (111).
In addition, because of the use of spur gears as the drive gear 103 and the driven gear 108 (109), these gears become thick. The ratio of the axial length of the weight 110 (111) to the sum of the axial length of the weight I 10 (1 I 1 ) and the axial length of the driven gear 108 (109) is therefore reduced. As the balancer apparatus is made more compact, the weights 110 and 111 will become too small to provide good vibration damping due to those restrictions.
Further, it is necessary to supply lubricating oil to the bushings 112 and 113 between the weights 110 and Ill and the support shafts 106 and 107 to smoothen the rotation of the weights 110 and 111. This balancer apparatus is not, however, provided with a means to supply lubrication oil to the bushings 112 and 113. Thus, the vibration reducing effect of weights 110 and ill is diminished.
In the above balancer apparatus, the bushings 112 and 113 are plate members that are bent so that their edges are bonded to each other. Thus, when the bushings 112 and 113 are installed into the respective support holes 116 and 117 of the weights 110 and 111, the juncture of the edges may damage the peripheral surfaces of the support shafts 106 and 107.
In order to reduce both the noise and wear created by the engagement of drive gear 103 and the first driven gear 108, there is a known method of supplying lubrication oil to the point where these gears contact. However, a change in the rotation of the crank shaft 101 displaces the drive gear 103. This method does not consider the influence of the displacement on the contact point between the drive gear 103 and the driven gear 108 when the rotational direction of the drive gear switches. Therefore, there is still a pending question as to how to effectively reduce a gear-hitting sound caused by a change in the rotation of the crank shaft 101.
Furthermore, unless the gap between the drive gear 103 and the driven gear 108 is held correctly at the designed value, a load which is applied to the crank shaft 101 to reduce the vibration of the engine would become insufficient, or backlash would occur. To keep the accurate gap between the gears 103 and 108, it is necessary to improve the working precision of that surface of the balancer case 105 which is to be attached to the cylinder block 104, or install a shim between the attaching face and the cylinder block 104. However, such countermeasures require much time and labor and require a plurality of shims with different thicknesses, thus increasing the manufacturing cost.
In addition, it is necessary to secure the support shafts 106 and 107 unrotatable to the balancer case 105 to avoid unnecessary friction therebetween. Accordingly, the support shafts 106 and 107 are generally pressed into the respective holes provided in the balancer case 105. It is, however, desirable that the balancer case 105 be made of a light alloy to become lighter, while the support shafts 106 and 107 should be formed of steel to keep the sufficient strength. While the engine is warmed, the difference between the coefficient of thermal expansion of the balancer case 105 and that of the support shafts 106 and 107 may form a gap therebetween, resulting in displacement of the center of each support shaft. In this regard, the support shafts 106 and 107 may be made of a material with a larger coefficient of thermal expansion than that of the balancer case 105. This method would, however, cause the support shafts 106 and 107 to overexpand, which may crack the balancer case 105.